Self-loading pressure accumulator



Patented Aug. 5, 1952 olii-fici;

SELF-LOADING PRESSURE AocUMULA'ron i A Matthew W. Huber, Watertown, Y., vassignorV y to The New York Air Brake Company, a corporation ofNew Jersey Application March s, i948,A serial No. 13,647

This invention relates to pressure accumulators and particularly tothe type in which the loading pressure is developed by compressed air.

Such accumulators are used on airplanes and in other locations where light weight is a prime consideration.. A `separator between the gas of the Acushion and the hydraulic liquid is necessary to prevent occlusion of gas in the liquid.

Diaphragme have been tried, but are short-lived, so that a piston is generally accepted as the most satisfactory separator. Leakage of liquid (oil) past such a piston into the cushion space has been a source of trouble. loss of gas (usually air) from the cushion.

The present invention provides automatic means to maintain cushion pressure and purge anyfoil accumulating in the cushion, returning such oil to the sump of the hydraulic system.

The invention is applicable to any system having a gas-cushion accumulator, and having a pressure line which is alternately subjected to operating hydraulic pressure and alower pressure. Usually the lower pressure is produced by venting the line.

According to the invention a hydraulically operated motor actuates a ,small compressor which charges the air cushion. The hydraulically operated motor makes one cycle each time the pressure line is loaded and then unloaded as it may be by a manually actuated control valve,

or by an automatic unloading valve, to name two expedients well known in the hydraulic circuit art. Each such cycle delivers a small increment of. air to the accumulator air cushion.

At a desired maximum cushion pressure a loaded relief valve starts to bleed the air cushion. The relief valve is so llocated as to purge hydraulic rliquid so long as any liquid `is present in the air cushion, and in the absence of liquidfto ldischarge excess air. kept up to pressure despite minor leakage, and is kept substantially free of liquid.

A preferred embodiment of the invention using one of many available pump-unloading valves will now be described by reference to the accompanying drawing.

Fig. 1 is a View partly in section and-partly in diagram showing a hydraulic circuit includv ing the self-loading accumulator.

here assumed to be a high speed displacement In this way the cushion is- 2 Claims. (Cl. 103--223) pump capable of discharging into line 4 against VVback pressures of the order of-1500 p.s. i. or

So also has been K higher.- Y

One branch of line li leads to the relief nvalve mechanism enclosed inv bodyi. This may-assume various forms. The one chosen for illustration is -a type developed by applicants assigneefand not claimable per se herein since it is not the invention ofthe presentapplicant. It need be .describedon'lybriefly c A unitary piston `valve comprising a lower piston head'i,` an intermediate valve head '1 -,rand an upper pistonhead 8 is axially shiitable'ias a unitin a Abore in body 5. 'Inthe lower position of the valve, head 'I isolates pressure chamber 9 (connected with discharge line li)- from relief chamber II which is drained to sump I by line I2. ,`In-- the upper position of valve head 'If the chambersV 9 and-I Iy communicate freely.

Pressure chamber 9 communicates .withW pressure line I3 past check valve I4. This valvewis lightly biased in a closingdirection by a' coil compression spring I5; Line I3; beyond valve :I4 is in free communication with space v I6 in housing 5 below pistonhead 6.' Hence pressure in line I3 urges Vvalve f1' in anopening direction, by lreacting upward on piston head 6. The downward and connection I2.`

motion of valve I is limited by a stop bossv on the lower end of piston head 6, so that the closed position' of valve head 'l is 'precisely defined; 1- i Theupper piston head 8y is formedjwith a iiat on .one side as indicated at Il. v'lhisoiers restricted communication', between chamber. 9 and the space above piston head 8. Guided in a cylindrical bushing I8 is a valve plunger I9 which is in thrust relation .with piston head '8, and is. smaller in diameter than said piston head. Plunger i9 carries a spring-seat 2| and `isvbiased downward by a coil compression spring 422 which reacts between spring-seat ZI. and an adjustable spring-seati' threaded into a tubular extension of housing `l5. In this way piston 6 and valve 'I are biased downward to valve-closed position. but the piston ivalve is hydraulically balanced except when the space above head 8 is vented;

. The valve plunger I9 has a flat atk 24 which extends only part way up one side` of the plunger.

,When opened by upward motion of plunger '.IS,

the vent passage so afforded has awlarger flow capacity than that oiered by the iiat lI onv head vi! so that thefpressures onheads ltand Sere-gun- Aeclual and the valve is forced up. A drain port 25 leads from the spring housing ,to chamber -II 'Whenpressure in line,` I3 isbelow a minimum head 6. When the back pressure in chamber I-9 'l reaches a value (here assumed. to be 150G-p. s. i.) ,4:

plunger I9 will have retreated far enough to expose flat 24, reducingrfthe--fpressure on the upper end of piston head V8. "Valve I Yis unbal-v anced and so quickly moves up and unloads pump-- 3. Check valve I4 immediately closes.V When pressure later falls to the assumed low value of 1200 p. s. i. port 24 will again closewhereupon the valve 'I will rapidly return to closed (loading) position.

-Thus the unloading valve responds sharply to changes of pressure in line I3. In loadingA position linev4 is subject to pressures between 1200 ^=and`l50`0 p. s. i. but in unloading position theA -pressure drops to nearly atmospheric.

The relief valve just described has outstanding operativecharacteristics for use with the selfloading accumulator, vto be described. It unloads the pump completely. It shifts quickly between `'loading and unloading positions and has no tend- Yency to stall in intermediate positions.

To 'steady theiaction of line. I3 as a source of .pressurefluidt is desirable to use an accumulator and' one isshown connected to line I3. This comprises a' cylinder26 closed at its ends by heads '21 'and' 28and-subdivided by afloating piston 129 .into a pressure liquid space '3I"to whichY line I3 is connected and algas cushion space. 32.

ToV show some device as typical of those which ...may be fed by line I3, la Vvalve generally indi- .cated at 33 is connected to'pressure line I3 and to an exhaust line 34. Aihandle 35 sets valve 33 -tozconnect aV motor v36 toA supply line I3 or eX- ...haustline V34'or disconnect it. from both.

Gas cushion accumulators'ias heretofore con- .structed have given trouble because of loss ofgas 1 Vfrom the. gas cushion space Y32 andbecause of ac- `Acumulation of hydraulic liquid in space 32, which occursas aresultof leakage past Ythe piston.

. To* overcome these diiculties a' pulsator vtype compressor is connectedfto be'operated'by the pressure .changes in line 4 and .deliver compressed gas (iusually air)` to cushion space 32.

A shouldered Acylinder .31 is bored in head 28. When air is to be used'as Vthe cushion gas an inlet poppet valve Y33 admits air'from atmosphere. Adi"scharge poppeil vali/'e 39 Vleads from the cylin- .lder 31 to space 32.

A plunger 4I is reciprocable in Ycylinder 3l Aand is lbiased in itsv suctionA direc- '..tionsby a coil spring 4'2 whichreacts on a ilange 40 smaller than the bore of the upper end of the cylinder. The outer-(larger) end of the .cylinder is closed by a head 43 and a branch of discharge line 4'1eads'to the fouter end ofthe cylinder. Thus each .time the'pump'3 is loaded l'the plunger 4I makes a displacement strokeand 4each' time 'the pump is unloaded the plunger 4I i makes a' suction stroke.

` By keeping the compressor clearance small, and

.fusing a light returnspring 42,'the pulsator comfpressor can be made 'to deliver against ka cushion pressure which is `Vrelatively high. Accumulator pressure is not as high as the maximum pressure vreached in line 4.. 'Plunger 4I makes its compresis satisiactoryior all ordinary purposes, and provides a less expensive structure; I am aware that a pulsator compressor can be constructed to deliver against a pressure higher than that of the motive-liquid. VlSuch a unit is illustrated in Fig. 2.

The cylinder I3'I is of two diameters and similar to cylinder 31. It is closed by head |43. A differential piston is used and comprises an airdisplacing plunger I4I working in the smaller bore of .the cylinder, anda motor piston. |40 t- .ting thelarger bore ofthe cylinder. The biasing spring |42 reacts against piston |40. The spring space is vented to atmosphere at I45. Air

.inlet and. discharge valves .are indicated at I 38 and I 39 respectively. Except that the pulsator piston isof the differential type the two constructions are substantially.. the same. They operate on the same principle.

Some general considerations will be stated to assure a correct understanding of the disclosure.

As a rule, the pressure maintained in an accumulator is much less than the maximum pressure developed by the pump. Cases are'known where it is as .low as one half of pump delivery pressure. lt is this fact whichmakes the compressor motor ofEig. 1 usually adequate. Where high cushion pressures are desired they can be developed and maintained by using the arrangement shown in Fig. 2.

For villustrative purposes an automatic relief valve 5 is shown and is described in considerable detail. It typifies any means which will alternately cause pressure to be developed and dissipated in line 4. It is illustrated as the best known means,.rst because this particular valve is-known to be automatic and certain in action, and second because its venting action is virtually cornplete. Obviously a hand operated vent valve could be used to secure the ultimate function of opening and closing a vent.

`What is claimed is:

1. The combination of a liquid supply; a hydraulic pressure accumulator comprising an enclosing shell and a movable abutment dividing the space within said shell into a liquid space and a gas-cushion space, said shell also enclosing a pocket in communication with said gas space to which any liquid entering the gas space tends to flow by gravity; means for controlling theow of liquid under pressure from the liquid space to a point of use; la constantly driven pump arranged to draw viiquid from said supply and deliver it at higher pressure; a delivery connection from the pump discharge to said liquidspace; a check valve interposed in said connectionA and serving to inhibit reverse flow therethrough; a normally closed valve operable to open and close a vent from the pump discharge in advance of said check valve; a motor compressor unit of the pulsator type, comprising a pulsator motor arranged to move in response to changes of pressure lin said delivery connection occasioned by operation of said vent valve, and a compressor arranged lto be actuated by motion of said motor and connected to deliver compressed gas to said gas-cushion space; and a loaded relief valve controlling a vent path from said pocket and arranged to open in response to excess pressure to discharge liquid when present and gas at other times.

2. The combination of a liquid supply; a hydraulic pressure accumulator comprising an enclosing shell and a movable abutment dividing the space within said shell into a liquid space and a gas-cushion space, said shell also enclosing a pocket in communication with said gas space to which any liquid entering the gas space tends to ilow by gravity; means for controlling the ow of liquid under pressure from the liquid space to a point of use; a constantly driven pump arranged to draw liquid from said supply and deliver it at higher pressure; a delivery connection from the pump discharge to said liquid space; a check valve interposed in said connection and serving to inhibit reverse flow therethrough; an unloader interposed in said connection between the pump and the check valve and serving in response to discharge pressure developed by the pump, to open and close a vent from the pump discharge in advance of said check valve as said pressure rises above a predetermined maximum 6 and falls below a predetermined minimum, respectively; a motor compressor unit of the pulsator type, comprising a pulsator motor arranged to move in response to changes of pressure in said delivery connection occasioned by operation of said unloader, and a compressor arranged to be actuated by motion of said motor and connected to deliver compressed gas to said gascushion space; and a loaded relief valve controlling a vent path from said pocket and arranged to open in response to excess pressure to discharge liquid when present and gas at other times.

MATTHEW W. HUBER.

REFERENCES CITED The following references are of record in the le of thispatent:

UNITED STATES PATENTS 

